linux-kernel - Re: [RFC] usb: host: xhci-mem: Write high first on erst base of secondary interrupter

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Date: Thu, 23 May 2024 16:38:48 +0300
From: Mathias Nyman <mathias.nyman@...ux.intel.com>
To: Jung Daehwan <dh10.jung@...sung.com>
Cc: Mathias Nyman <mathias.nyman@...el.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Subject: Re: [RFC] usb: host: xhci-mem: Write high first on erst base of
 secondary interrupter

On 23.5.2024 7.43, Jung Daehwan wrote:
> On Wed, May 22, 2024 at 04:40:56PM +0300, Mathias Nyman wrote:
>> On 22.5.2024 4.03, Daehwan Jung wrote:
>>> ERSTBA_HI should be written first on secondary interrupter.
>>> That's why secondary interrupter could be set while Host Controller
>>> is already running.
>>>
>>> [Synopsys]- The host controller was design to support ERST setting
>>> during the RUN state. But since there is a limitation in controller
>>> in supporting separate ERSTBA_HI and ERSTBA_LO programming,
>>> It is supported when the ERSTBA is programmed in 64bit,
>>> or in 32 bit mode ERSTBA_HI before ERSTBA_LO
>>
>> xHCI specification 5.1 "Register Conventions "states that 64 bit
>> registers should be written in low-high order
>>
>>>
>>> [Synopsys]- The internal initialization of event ring fetches
>>> the "Event Ring Segment Table Entry" based on the indication of
>>> ERSTBA_LO written.
>>>
>>
>> Any idea if this is a common issue with this host?
>> Should other 64 bit registers also be written in reverse order.
>>
>>> Signed-off-by: Daehwan Jung <dh10.jung@...sung.com>
>>> ---
>>>   drivers/usb/host/xhci-mem.c | 5 ++++-
>>>   drivers/usb/host/xhci.h     | 6 ++++++
>>>   2 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
>>> index 3100219..36ee704 100644
>>> --- a/drivers/usb/host/xhci-mem.c
>>> +++ b/drivers/usb/host/xhci-mem.c
>>> @@ -2325,7 +2325,10 @@ xhci_add_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir,
>>>   	erst_base = xhci_read_64(xhci, &ir->ir_set->erst_base);
>>>   	erst_base &= ERST_BASE_RSVDP;
>>>   	erst_base |= ir->erst.erst_dma_addr & ~ERST_BASE_RSVDP;
>>> -	xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
>>> +	if (intr_num == 0)
>>> +		xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
>>> +	else
>>> +		xhci_write_64_r(xhci, erst_base, &ir->ir_set->erst_base);
>>
>> This may cause issues with other hosts expecting low-high order as stated
>> in the specification.
>>
>> If all 64 bit registers should be written in high-low order for this host then
>> maybe set a quirk flag and change xhci_write_64()instead.
>>
>> xhci_write_64(...)
>> {
>> 	if (xhci->quirks & XHCI_WRITE_64_HI_LO)
>> 		hi_lo_writeq(val, regs);
>> 	else
>> 		lo_hi_writeq(val, regs);
>> }
>>
> 
> Mathias, Thanks for the comment.
> 
> I've seen this issue only writing the base address of ERST.
> It's better to use a quirk flag as you said.
> How about using the quirk only in xhci_add_interrupter?
> 
> @@ -2325,7 +2325,10 @@ xhci_add_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir,
>    	erst_base = xhci_read_64(xhci, &ir->ir_set->erst_base);
>    	erst_base &= ERST_BASE_RSVDP;
>    	erst_base |= ir->erst.erst_dma_addr & ~ERST_BASE_RSVDP;
> 	xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
>   	if (xhci->quirks & XHCI_WRITE_64_HI_LO)
> 		xhci_write_64_r(xhci, erst_base, &ir->ir_set->erst_base);
> 	else
> 		xhci_write_64(xhci, erst_base, &ir->ir_set->erst_base);
> 

This works.
Maybe even skip the xhci_write_64_r() helper and just use hi_lo_writeq() directly.

Thanks
Mathias